A glass disc is installed in the production tubing prior to completion of horizontally drilled oil and gas wells as a means to temporarily isolate areas having different pressures during testing and completion of the well. The glass disc is an obstruction to hydraulic communication with a reservoir of oil or gas after the completion of the well. Completion requires that the glass disc be removed in order to begin production of hydrocarbons from the reservoir.
Christmas trees and wellhead isolation tools, the latter commonly known as tree savers are used at the end of the tubing string at the earth's surface to control the produced hydrocarbons and the fluids introduced into the wellbore. The pressure ratings for tubing used to seal and control fluid flow to and from a well varies from one manufacturer to another. Tubing is rated for both its burst pressure and collapse pressure. A typical oil production tubing can have a burst pressure rating of 8430 psi and collapse pressure rating of 7500 psi.
Christmas trees constructed of a series of pipes and valves are located on the wellhead after the drilling of the well has been completed. Christmas trees are not designed to withstand the high pressures generated in pumping operations. This limitation serves as a restriction on the hydraulic pressure that can be applied to rupture the glass disc positioned downhole on the production tubing.
Various mechanical and hydraulic devices have been used to provide a means for rupturing the glass discs used to temporarily seal the end or a section of tubing. However, the devices known to the art are complex in construction and require various special tools and lines, can require significant time for set-up and may not fracture the disc on the first try.
It is therefore an object of the present invention to provide an improved method for rupturing a glass disc positioned in a section of production tubing in a well that is reliable and simple to perform, provides a clear indication that the disc has been removed and that does not involve complex downhole apparatus and controls.
It is another object of the present invention to provide a method to rupture a glass disc positioned in a well for isolation of areas having different pressures while protecting the wellhead Christmas tree and production tubing from the higher and potentially damaging pressure used in the rupturing process.